What is the iPrEx study?

iPrEx (also known as the Chemoprophylaxis for HIV Prevention in Men trial or the PrEP Initiative) was the first study to report data on the effectiveness of oral PrEP, the use of a pill usually used to treat HIV infection to reduce HIV infection risk, in people. The initial iPrEx results were reported in November of 2010 in the New England Journal of Medicine.

iPrEx found that daily use of the antiretroviral drugs combination emtricitabine 200 mg. and tenofovir 300 mg. (FTC/TDF), also known as Truvada®, provides 99% protection against HIV infection in MSM, when taken seven days a week.

iPrEx was a double blind placebo controlled trial, meaning that half of the study participants received Truvada and half received a placebo (blank pill). Neither the study participants nor the investigators knew which participants received the drug or the placebo. More information about Truvada is available here.

iPrEx enrolled 2,499 participants at 11 sites in 6 countries (Brazil, Ecuador, Peru, South Africa, Thailand and United States) on 4 continents. 1,251 participants were assigned to FTC/TDF (Truvada) and 1,248 were assigned to take a placebo tablet (blank pill). The iPrEx study started in June of 2007 and concluded in February of 2011. Participants were followed for a median of 21 months.

As in other HIV prevention trials, participants’ sexual risk behaviors decreased after enrolling in the study. Participants in the iPrEx study increased their use of condoms and decreased their number of sexual partners.